The present invention relates to a medical tube with excellent quality and, more specifically to a medical tube particularly suitable as an artificial blood vessel of medium or small diameter.
It has been conventional to practice blood vessel replacement or perform a bypass operation using an artificial medical tube which is compatible with organic tissues, as described, for example, in U.S. Pat. No. 4,173,689, as a radical operation for securing and achieving the functions of a diseased ureter, trachea, esophagus or blood vessel.
Typical medical tubes include one prepared by knitting or weaving a polyester fiber into the form of a tube, and then crimps are provided thereto as described in Japanese Unexamined Patent Publication No. 94699/1977; or one prepared by forming polyethylene tetrafluoride into the form of a tube, followed by stretching to impart thereto a fibrous microstructure as described in Japanese Unexamined Patent Publication No. 7284/1971, etc.
These medical tubes are still not satisfactory, although relatively good results are obtained when they are applied as an artificial ureter, trachea, esophagus or blood vessel having an inner diameter of 10 mm or more. In artificial blood vessels having small inner diameters of 7 mm or less, particularly 6 mm or less, patency results are extremely poor, and a tube obtained from polyethylene tetrafluoride by imparting porosity to the tube has only been used for limited purposes.
Clinicians earnestly desire completion of an artificial blood vessel which is applicable as a peripheral artery having an inner diameter of 3 to 4 mm, since it can be used widely for such purpose as a bypassing vehicle in coronary artery operations. While various studies are being made recently on medium and small diameter blood vessels, no such vessels are currently available.
With the above artificial blood vessel obtained by knitting or weaving a polyester fiber, a thrombotic layer of as thick as 1 mm may be formed in the internal cavity thereof. Accordingly, if this material is used as a medium or small diameter blood vessel, its internal cavity or channel will soon become obstructed by the formation of thrombi.
Thus, it is a prerequisite for the material itself to have a sufficient antithrombotic property and is not obturated by the initial thrombi formation.
A number of artificial blood vessels having different end faces and internal surface structures were made for testing purposes using several kinds of polyether polyurethanes or polyurethane ureas having different antithrombotic properties. As a result of implantation experiments with dogs using the above artificial blood vessels, it has been found that the obturation can be entirely attributed to the panni at the sutured portion.
The expression, pannus (panni), used herein means a granulation which has grown from the cut end of an organ wall of a living body at a portion where the organ of a living body has been cut and anastomically connected with a medical tube growth of the panni toward the internal cavity causes turbulence in the flow of blood and the like which passes therethrough. Particularly in artificial blood vessels, if pannus grows in that portion where the blood flow is transferred from the organic blood vessel to the artificial blood vessel, namely at the center side of the sutured portion, blood stagnation is created immediately after the formation of the pannus, and accumulating thrombi gradually becomes organized and enlarged. As a result, the effective sectional area of the internal cavity, as well as blood flow rate, may decrease, and finally the inside of the artificial blood vessel will become completely obturated with thrombi.
This formation of pannus is due to the self-recovering function of the cut tissue, while which is essentially unavoidable, the growth of which is particularly remarkable when the section is contacted with a foreign body. Accordingly, if the anastomosis or connection of an organ of a living body with an artificial medical tube is achieved without contacting the sections thereof with each other, growth of panni can be inhibited.
The artificial medical tube of the present invention which dilates at the cut ends toward its external surface can be sutured with an organ of a living body without its cut ends being in contact with each other. This inhibits growth of panni and exhibits excellent patency.
Also, medical tubes have been provided which have been formed to have a predetermined length preliminarily with both ends being dilated toward the external surface thereof. However, since such medical tubes are required in a variety of lengths depending on the patients needs, it is not practically possible to have tubes always in hand over a wide variety of lengths.